INHERITANCE IN HYDATINA 



57 



the curve of hatching is similar to a probability curve, the varia- 

 biUty of the hatching time may be measured by the standard 



deviation. This is obtained by the formula <r = \l ^^, in 



>! n 



which p is the number hatching each day, a the deviation from 



the mean duration of the egg stage, and n the total number 



hatching. The standard deviation in this case, as shown at the 



bottom of table 3, is 2.83 (days). A comparatively low standard 



deviation indicates that the hatching occurred within a brief 



period. A certain correction may be necessary, but this will be 



mentioned later. 



D X D. Females of line D were mated with males of the same 



Hne October 22 to 31, 1911. From 32 matings thus made, 543 



eggs, or 16.9 per female, were secured. These eggs were kept 



under observation until December 20, during which time 29, 



or 5.3 per cent hatched. There was great variability in the 



hatching time of these 29 eggs, that is, the hatching was spread 



nearly evenly over four weeks, with scattering ones later, as 



shown in table 4, instead of over two weeks as in C X C. This 



is shown by the high standard deviation, o- = 10.78. 



TABLE 4 

 Showing number of eggs that hatched, out of 543 in lot D X D, figure 1 



Percentage of viable eggs 5.3 



Standard deviation : o-h = 10.78 o-l = 3.64 



